The present invention relates to a magnetic disk drive apparatus to record data in a magnetic disk memory by a magnetic head mechanism having read/write and erase heads.
Generally, a magnetic disk drive apparatus comprises a spindle drive section to rotate a spindle on which a magnetic disk is mounted, and a carrier drive section to move a carrier on which the magnetic head is mounted in radial direction of the magnetic disk. This magnetic disk drive apparatus is coupled to a host computer and enables data to be written in a desired location on the magnetic disk and enables data to be read out from a desired location, by controlling the operations of the spindle drive section and carrier drive section in accordance with control data to be generated from the host computer.
The magnetic head to be used in this kind of magnetic disk drive apparatus has a read/write head section 2 and an erase head section 3 which are mutually disposed with a predetermined distance along the rotation direction of a magnetic disk 1, as shown in FIG. 1. In the write-in mode, the magnetic disk 1 is rotated in the direction indicated by an arrow in FIG. 1 and data is written in a track 4 of the magnetic disk 1 by the read/write head section 2, and at the same time the data previously written in the region out of the track 4 is erased by the erase head section 3. In this case, since the read/write head section 2 and the erase head section 3 are disposed apart from each other, in order to make the recording range by the read/write head section 2 coincide with the erasing range by the erase head 3, it is necessary to delay the operation start and stop timings of the erase head section 3 by a proper delay time with respect to the operation start and stop timings of the read/write head section 2. Now, the distance between the read/write head section 2 and the erase head section 3 is fixed, while circumferential speeds at the outermost peripheral and innermost peripheral tracks of the magnetic disk 1 differ; therefore, the above-mentioned proper delay times would differ in the cases where the magnetic head is on the outermost peripheral and innermost peripheral tracks. Namely, in the case where the magnetic head is on the outermost peripheral track, the above-mentioned proper delay time is set to be shorter than that in the case where the magnetic head is on the innermost peripheral track. Thus, in order to erase every data in the track edge region by the erase head section 3, for example, it is required to set the delay time relating to the operation start timing of the erase head section 3 to be equal to the optimum delay time which is set in the case where the magnetic head is on the outermost peripheral track; in addition, it is necessary to set the delay time with respect to the operation stop timing of the erase head section 3 to be equal to the optimum delay time which is set in the case where the magnetic head is on the innermost peripheral track. However in this case, if the magnetic head is on the innermost peripheral track, the erasing operation will be started early, while if the magnetic head is on the outermost peripheral track, the erasing operation will be stopped at a later timing. For example, when the central axes of the read/write head section 2 and the erase head section 3 are out of the central axis of the track, i.e., when the magnetic head is in the off-track position, the data which has been previously written will be partially erased.
In addition, there is conventionally known a magnetic disk drive apparatus having two magnetic heads 5 and 6 which are disposed to face each other with respect to the magnetic disk 1 so that data can be recorded on both sides of the magnetic disk 1. Head sections 5A and 6A of these magnetic heads 5 and 6 are disposed apart from each other in the radial direction of the magnetic disk 1. For example, the head section 5A of the magnetic head 5 which is arranged on one surface side of the magnetic disk 1 is disposed in a position which is shifted by a few tracks in the outer peripheral direction of the magnetic disk 1 as compared with the head section 6A of the magnetic head 6, which is arranged on the other surface side of the magnetic disk 1. This is because pad sections 6B and 5B to support the portions of the magnetic disk 1 on the opposite sides of the head sections 5A and 6A, are formed integrally with the head sections 6A and 5A, respectively. In addition, in the case where the numbers of tracks on both sides of the magnetic disk 1 are equally set, the outermost peripheral track on the one suface side of the magnetic disk 1 is formed to be out of position by a predetermined number of tracks outwardly from the outermost peripheral track on the other surface side. On the contrary, the innermost peripheral track on the other surface side is formed to be out of position by a predetermined number of tracks in the inside direction from the innermost peripheral track on the one surface side.
In the magnetic disk drive apparatus of the above kind, the delay times with respect to the operation start timings of the erase head sections of the magnetic heads 5 and 6, are set to be equal to the optimum delay time which is set in the case where the magnetic head 5 is on the outermost peripheral track on the one surface side of the magnetic disk. On the other hand, the delay times relating to the operation stop timings of the erase head sections, are set to be equal to the optimum delay time which is set in the case where the magnetic head 6 is on the innermost peripheral track on the other surface side of the magnetic disk. Due to this, all the data in the track edge region may be erased. However, as described above, if the delay times with respect to the operation start and stop timings of the erase head sections are set, part of the data which has been previously written will be erased over a wider range as compared with the previously-mentioned one-side recording method. In the case where the magnetic head is set in the off-track state, it may be impossible to correctly the read out data which was partially erased.
Further, in the magnetic disk drive apparatus of this kind, each track is divided into a plurality of sectors, and read/write operation is effected for each sector. The adjacent sectors are divided by a gap area so that data stored in the adjacent sectors may not affect each other. The number of bytes alloted for the gap area is determined in accordance with the degree of fluctuation in rotation of a disk driving motor, and the delay times of the operation start and stop timings of the erase head section. It is required to decrease the number of bytes for the gap area in order to increase the amount of data to be stored in each track. Therefore, it is important to shorten the delay times of the erase head section.